Stack Gas Heat Recovery and Ethanol Extraction System
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Solution Overview
Problem
Bakeries face economic and environmental challenges due to low oven efficiency from waste heat loss and pollutant emissions in stack gas, with existing solutions like oxidizers being costly and inefficient for ethanol recovery.
Innovation Solution
A system incorporating a gas-gas heat exchanger, double-film-wise heat exchanger, condenser/heat exchanger, and ethanol recovery unit to extract and recover water-soluble gases and waste heat, utilizing a fog generator for ethanol diffusion into water droplets, and a water treatment unit for separation and reuse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If oxidizing equipment is installed to burn pollutant emissions in stack gas, then compliance with EPA regulations is achieved, but additional fuel consumption increases and heat losses increase
Solution Approach 1:
The patent converts the harmful ethanol emissions in stack gas into a beneficial fuel source by capturing and condensing the ethanol, then burning it in the oven. This eliminates the need for separate oxidizing equipment while reducing overall fuel consumption, as the recovered ethanol supplements the fuel supply.
Solution Approach 2:
Instead of discarding the ethanol-containing stack gas through oxidizers, the system recovers the ethanol through condensation and reuse it as fuel in the oven, transforming waste into a valuable resource.
2Loss of substance
If condensation process is used to remove ethanol from stack gas, then ethanol recovery is achieved, but water vapor condensation occurs and ethanol diffusion is insufficient at higher temperatures
Solution Approach 1:
The condensation process is divided into multiple stages: first cooling the stack gas to condense water vapor, then further cooling to condense ethanol. This segmented approach allows selective condensation of different components at different temperature levels, improving ethanol recovery efficiency.
Solution Approach 2:
The patent introduces a vertical dimension to the condensation process by using a packed column where condensate flows downward while gas flows upward, creating counter-current contact that enhances mass transfer and ethanol diffusion into the condensate.
3Loss of substance
If stack gas is cooled below dew point to condense ethanol, then ethanol absorption increases, but water vapor condenses out and ethanol concentration remains low
Solution Approach 1:
The system extracts water vapor from the stack gas through condensation before ethanol condensation occurs. By removing the bulk water vapor first, the subsequent ethanol condensation produces a more concentrated ethanol solution, improving recovery efficiency.
Solution Approach 2:
The system performs preliminary cooling and water vapor condensation before ethanol condensation. This preliminary action prepares the gas stream for more efficient ethanol recovery by reducing the volume of water that would otherwise dilute the ethanol condensate.
4Productivity
If multiple heat exchangers and recovery units are installed, then waste heat and ethanol recovery efficiency increases, but system complexity increases
Solution Approach 1:
The patent combines multiple functions into integrated units: the condenser serves both as a heat exchanger and an ethanol recovery device, while the packed column performs both cooling and ethanol absorption. This merging reduces the number of separate components needed while maintaining high recovery efficiency.
Solution Approach 2:
The heat exchangers in the system perform multiple functions: cooling the stack gas, condensing water vapor, recovering waste heat for preheating combustion air, and facilitating ethanol condensation. This multi-functionality reduces overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system optimizes the recovery of waste heat, water vapor, and ethanol, reducing fuel consumption by up to 50% and eliminating the need for oxidizers, while providing supplemental fuel and reducing carbon emissions.
Implementation Method 1
a gas-gas heat exchanger for cooling hot stack gas from the oven to a temperature higher than the dew point of the hot stack gas, and for transferring the removed heat to pre-heat combustion air
Implementation Method 2
a double-film-wise heat exchanger for receiving the cooled stack gas from the gas-gas heat exchanger, the double-film-wise heat exchanger comprising cooling and heating channels running in counter-flow directions, in which a thin film of liquid is formed or induced on each side of a common heat transfer wall
Implementation Method 3
an ethanol recovery unit for receiving the cooled stack gas from the condenser/heat exchanger, the ethanol recovery unit comprising a special fog generator for spraying water in several water droplet clouds at an angle to a horizontal plane, wherein the clouds of water droplets descend through the ethanol recovery unit and fall to the bottom, and the cooled stack gas enters the ethanol recovery unit and is released into the droplet cloud tangentially
Implementation Method 4
a water treatment unit for receiving the water and cooled stack gas condensate from the ethanol recovery unit, the water treatment unit comprising filters for separating water from ethanol, oil, or solid particles
Data Source
AI summary
An apparatus and method for extracting and recovering water-soluble gas and waste heat from an oven is provided. The method employs a gas-gas heat exchanger for cooling hot stack gas from the oven to a temperature higher than the dew point of the hot stack gas, a double-film-wise heat exchanger for receiving the cooled stack gas from the gas-gas heat exchanger, a condenser/heat exchanger for receiving and further cooling the stack gas from the double-film-wise heat exchanger to ambient temperature by heating a utility water stream, which can then be used for hot water and steam process services, and an ethanol recovery unit for receiving the cooled stack gas from the condenser/heat exchanger.